The present invention concerns a catalyst composition and its use for hydrogen processing hydrocarbons. In one specific aspect, the invention concerns a catalyst containing the fibrous form of the mineral imogolite and its use for demetalizing and deasphalting heavy petroleum fractions.
Heavy hydrocarbon fractions such as petroleum residua, bitumen, coal and shale oils, and the like, are known to contain substantial amounts of contaminants such as sulfur, nitrogen and metals, especially nickel and vanadium. Such heavy fractions also typically contain a substantial fraction of heat-sensitive, normal heptane-insoluble hydrocarbonaceous material conventionally termed "asphaltenes".
It has been suggested to upgrade contaminated heavy oil fractions by hydrogen processing in order to remove the metals, sulfur and nitrogen, but the presence of asphaltenes in the oils often has an adverse effect on the activity of conventional hydroprocessing catalysts. Another problem encountered in conventional heavy oil hydroprocessing when large concentrations of metals are present in an oil, is that the metals tend to deposit rapidly on the catalyst surface and plug the pores of conventional hydrogen processing catalysts, with a consequent loss of catalytic activity for sulfur and nitrogen removal. This has led to the suggestion that demetalizing guard beds should be used upstream of a hydrodesulfurizing and/or hydrodenitrifying reactor.
Because of the tendency of metals to deposit on the surfaces of hydrocarbon processing catalysts during processing of heavy oils and the tendency of metals to plug the pores of the catalysts, it is desirable to employ a hydrodemetalation catalyst having a large fraction of its total pore volume provided by pores having a diameter of greater than 200 Angstrom units, which are termed "macropores" herein. Manufacture of satisfactory catalysts with a substantial fraction of total pore volume in macropores is difficult, in that most catalysts with a satisfactory pore size distribution for demetalation are quite deficient in crush strength and attrition resistance. The shaping procedures used for forming suitable catalytic bodies also often have an adverse effect on the macropores content of catalysts.
In order to overcome the adverse effects of asphaltenes on hydrogen processing catalysts, e.g. from rapid coking and from inhibition of hydrodesulfurization, it has been suggested to use a solvent treatment to separate asphaltenes prior to hydrodesulfurization or hydrodenitrification. The non-asphaltenes may be dissolved in a liquefied light aliphatic, such as propane, while the insoluble asphaltenes are rejected. Not only is solvent deasphalting relatively complex and expensive, but it also has the disadvantage of rejecting potentially valuable hydrocarbonaceous materials, since asphaltenes can potentially be at least partially converted by hydrocracking, catalytic cracking and the like. Thus, the larger the fraction of asphaltenes in a given oil, the less attractive solvent deasphalting becomes.
U.S. Pat. No. 4,152,250 suggests the use of a catalyst containing sepiolite (Meershaum) and transition metals and/or Group IIB metals for hydrotreating and hydrodemetalizing hydrocarbons. Sepiolite is a magnesium silicate clay.
U.S. Pat. No. 4,166,026, suggests a two-stage process for hydrogen treating heavy hydrocarbon oils. In the first stage, a catalyst is employed which contains such naturally occurring magnesium silicates as sepiolite, attapulgite or palygorskite or synthetic products closely related to these minerals in composition and structure, supporting metals from Groups VA, VIA and VIII. employed. The catalyst employed in the second conversion stage uses a carrier having at least 90% of its pore volume provided by pores having diameters of 35-200 Angstrom units, supporting metals from Groups VA, VIA and VIII.
The catalysts using magnesium silicates as supports which are described in U.S. Pat. No. 4,152,250 and U.S. Pat. No. 4,166,026, are preferably prepared by grinding the mineral to small size particles and then kneading an aqueously moistened dough formed from the mineral, after which the support is shaped.
Imogolite is a naturally occurring, clay-like mineral which has a fibrous, thread-shaped morphology. It is described on pages 359-364 of The Electron-Optical Investigation of Clays, J. A. Gard Ed., published by the Minerological Society, Great Britain (1971). Its composition is approximately 1.1 SiO.sub.2. Al.sub.2 O.sub.3.2.3 to 2.8 H.sub.2 O. It can be synthesized, for example, as described in Belgian patent publication No. 865,317.